The invention concerns a microphone module for a hearing aid device with a microphone carrier to which a plurality of microphones are attached, as well as a method to produce such a microphone module.
For cosmetic reasons, there is with hearing aid devices the desire for an extensive miniaturization of the devices. Furthermore, the devices should be as cost-effective as possible. In order to be able to achieve these goals, high standards are employed in the production and test methods. The generation of individual modules that can be prefabricated before the assembly of the hearing aid device, and also can be individually tested first with regard to their functionality, represents a possibility for lowering the production costs of a hearing aid device.
Hearing aid devices are known with a plurality of microphones that are arranged on a common carrier, and thus form a microphone module that can be integrated as a structural unit in the housing of a hearing aid device, or can be connected with a housing of a hearing aid device. For example, German patent document DE 196 35 229 A1 shows such a hearing aid device.
Components are known from the electro-technical industry in which injection-molded plastic moldings are provided with three-dimensionally directed conductor traces. These components are designated as MID (Molded Interconnect Devices) and, for example, used as chip sockets or plug connections. The MID technology allows mechanical and electronic functions to be combined in a component. Mostly thermoplastic synthetics serve as a base material, however duroplasts [thermosetting materials] or elastomers are also used. The conductor traces are, as a rule, applied directly to the component via metallization. Further electronic components (resistors, capacitors, etc.) can subsequently by applied via gluing or soldering.
A modular hearing device with a microphone, a receiver, an amplifier and a battery is known from German patent document DE 691 11 668 T2, in which the microphone is incorporated into a microphone module, the receiver is incorporated into a receiver module, the amplifier is incorporated into an amplifier module, and the battery is incorporated into a battery module. The individual modules can be removably connected with one another via dovetail-shaped connections. The electrical connection of the individual modules ensues by way of a flexible circuit board that is soldered with contact points of the modules.
A hearing device is likewise known from U.S. Pat. No. 6,456,720, in which a plurality of components are electrically connected with one another via a flexible circuit board.
As to the formation of conductor traces, various methods for metallization and structuring of the synthetic carrier are known, in particular from MID technology, of which the common ones are be briefly mentioned:
In heat stamping, the synthetic substrate is metallized and structured in one step. With a stamping die on which the positive conductor pattern is applied, a copper stamping foil with an intermediate bonding layer is pressed under pressure and the addition of heat onto the synthetic substrate. The substrate is melted on the surface via the heating effect. The conductor traces are cropped from the copper foil and connected with the substrate.
In metal-backed injection, a structured conductive pattern develops on a foil via screen or pad printing of a primer. During a conditioning process under temperature, the primer undergoes a chemical connection with the substrate surface and provides for a good bond strength. In this process, the foil is simultaneously formed. The foil is subsequently placed in an injection molding machine and back-injected. After the back-injection, the conductor traces are galvanically strengthened and refined.
In the two-component injection molding method, the structure of the conductive pattern is produced with a first injection molding made of metallizable synthetic that serves as a substrate for the chemical metallization. Depending on the synthetic, the surface must be treated again after the first injection molding. The small injection is newly inserted/loaded into a mold and extrusion-coated with non-metallizable synthetic. The free remaining conductor traces are subsequently chemically metallized and enriched.
In the masking method, the metallization of the synthetic carrier ensues via chemical coating. A synthetic injection molding part serves as a substrate in which the surface is initially prepared via corrosion or, respectively, etching for the next step of the process. The metallization subsequently ensues. A photoresist is applied for structuring and exposed with UV light via a three-dimensional mask. After development of the photoresist, the uncovered metal layer is galvanically strengthened and coated with an etching mask. After removal of the photoresist, the remaining metal is etched away and the surface is subsequently enriched.
In contrast to the masking method, in direct laser structuring the etching resist is directly structured with the laser. At the points at which the etching resist was removed by the laser, the metal is etched away. The surface is subsequently enriched.
In the LPKF laser direct structuring method, which is named after the company LPKF, a synthetic part is first injection molded. The transfer of the structure pattern subsequently ensues with a writing or imaging laser system. The subsequent metallization ensues in a chemically reductive bath.